Why You Can’t Treat Q&T Plates Like Mild Steel
Quenched & Tempered (Q&T) steel plates — such as S690QL, A514, Dillimax 690T, HITEN 780LE, and HIND Q&T — are not regular steels.
These plates are heat-treated to achieve:
- Yield strength between 690–1100 MPa
- Superior toughness and impact resistance
- Uniform hardness and fatigue life
But this very strength also makes them sensitive to heat and cutting methods. Incorrect processing can:
- Destroy the plate’s microstructure
- Cause edge cracking or HAZ hardening
- Reduce weldability and performance
Cutting Q&T Steel Plates – Do’s and Don’ts
| Cutting Method | Recommended? | Notes |
|---|---|---|
| CNC Plasma Cutting | ✅ Best choice | Clean, consistent; minimal HAZ if done with right settings |
| Laser Cutting | ✅ (thin plates) | Precise; best for ≤16 mm thickness |
| Oxyfuel / Gas Cutting | ⚠️ Conditional | Can cause edge hardening; must preheat >50 mm thick plates |
| Waterjet Cutting | ✅ Safe method | No heat-affected zone; good for complex shapes |
| Manual Torch Cutting | ❌ Avoid | High risk of uncontrolled HAZ and microcracks |
Best Practices for Cutting Q&T Plates
- Preheat thick plates (>40 mm) to 150–200°C before oxy cutting
- Keep cutting speed steady to avoid thermal overload
- Use dry, clean air for plasma systems to avoid edge contamination
- Inspect edges for cracks or hardness after cutting
- If CNC cutting complex parts, use nesting software to optimize layout and minimize heat distortion
Why Welding Q&T Steel Needs Extra Care
Quenched and tempered plates are highly engineered — and incorrect welding can reverse the tempering effect, causing:
- Edge brittleness or cracking
- HAZ (heat-affected zone) embrittlement
- Hydrogen-induced cracking after cooling
- Loss of mechanical strength near the weld area
That’s why welding Q&T steels like S690QL, A514, HIND Q&T is all about controlled heat input, proper filler selection, and avoiding post-weld heat treatment.
Welding Procedure – Step-by-Step
| Step | Q&T Plate Best Practice |
|---|---|
| Preheat | 100–150°C (for ≥20 mm thick plates) to reduce cracking risk |
| Cleaning | Clean edges with a stainless brush or grinder before weld |
| Filler Metal | Use low hydrogen consumables (E7018, E11018-G, etc.) |
| Interpass Temp | Maintain ≤150°C to avoid overtempering the base steel |
| Welding Type | GMAW (MIG/MAG), SMAW (Stick), or SAW (Submerged Arc) |
| Passes | Use multiple small passes instead of one hot pass |
| Cooling | Slow and uniform air cooling only – NO water quench or fan |
Do NOT perform post-weld heat treatment (PWHT) — it can destroy the tempered microstructure and cause significant loss of strength.
Filler Material Selection for Common Q&T Grades
| Q&T Grade | Suggested Filler Metal | Standard Designation |
|---|---|---|
| S690QL / HIND Q&T 690 | E11018-G, ER110S-G | AWS A5.5 / EN 12534 |
| S890QL / Dillimax 890 | E12018-M or ER120S-G | For high-strength joints |
| A514 Grade B | E10018-D2, ER100S-G | Match tensile properties |
| HITEN 780LE | E9018-G, ER90S-B3 | Prequalified filler |
Check with your welding electrode manufacturer for tensile matching, impact value, and diffusible hydrogen specs
Avoiding Common Q&T Welding Mistakes
Don’t:
- Skip preheat (especially on thick plates)
- Use generic mild steel rods
- Overheat the joint — it softens the HAZ
- Weld in open humidity without drying rods
- Leave uncleaned flame-cut edges before welding
Do:
- Use controlled, consistent heat
- Use tested low-hydrogen filler
- Confirm CE value from the MTC
Ask for a Welding Procedure Specification (WPS) for your grade
Post-Weld Inspection for Q&T Steel Structures
After welding, it’s essential to confirm structural integrity through non-destructive testing (NDT). Recommended methods include:
| Inspection Type | Purpose |
|---|---|
| Ultrasonic Testing (UT) | Detects subsurface weld cracks or voids |
| Magnetic Particle Testing (MPT) | Finds surface cracks in weld and HAZ |
| Dye Penetrant Test (DPT) | Reveals fine surface flaws on cut or weld edges |
| Hardness Test (optional) | Confirms no over-hardening in HAZ zone |
Also verify cooling was uniform, no distortion occurred, and weld beads match design dimensions.
Sourcing Weld-Ready Q&T Plates in India
Fabricators, OEMs, and EPC contractors can now source pre-cut, weld-tested Q&T plates from Indian suppliers like:
Hindustan Steel Corporation
- HIND Q&T Grades: 690, 890, 960
- CNC profiling + chamfered/bevel edges
- Supplied with MTC, CE value, impact test & weld guide
- Export-ready packaging + mill traceability
15 FAQs – SEO & Voice Search Optimized
What is the best method to cut Q&T steel?
CNC plasma or waterjet cutting is safest. Oxyfuel can be used with preheat for thick plates.
Why is welding Q&T steel difficult?
Because the heat-affected zone can lose strength if heat input is too high or uncontrolled.
Should I preheat Q&T steel before welding?
Yes, especially above 20 mm thickness. Preheat reduces cracking and hydrogen absorption.
Which welding electrodes work for S690QL?
E11018-G or ER110S-G are commonly used. Use low hydrogen variants only.
Can I laser cut S690QL?
Yes, especially for plates below 16 mm. For thicker plates, plasma or waterjet is safer.
Is post-weld heat treatment allowed on Q&T steel?
No. It can reverse tempering and destroy mechanical properties.
What happens if I overheat Q&T while welding?
It weakens the plate and makes the HAZ brittle — leading to possible cracking.
Can I use normal mild steel filler wire for Q&T plates?
No. You need tensile-matching low-hydrogen filler rods or wire.
What is the interpass temperature limit for Q&T plates?
Generally ≤150°C for S690QL and similar grades. Stick to WPS guidelines.
How do I clean Q&T edges before welding?
Use a grinder or stainless wire brush. Avoid contamination or scaling.
Are cut edges of Q&T plates weldable?
Yes, if cut properly. Flame-cut edges may require grinding or cleaning first.
Can Q&T plates be bent after cutting?
Yes, within allowable radius. Overbending can cause edge cracking — hot forming is safer.
Where can I buy pre-cut weldable Q&T plates in India?
From Hindustan Steel Corporation — with full QA docs and cutting service.
Do Q&T plates come with a welding guide?
Yes. Suppliers like HIND provide CE values, WPS support, and recommended filler selection.